Block copolymers are important components of materials for a variety of applications such as dispersants, crosslinkers, curing agents, resists, compatibilizers, inks, paints and surfactants. In particular, there is a wide range of potentially useful properties and applications for block copolymers of nylon 6 [see e.g. Bouma et al (Polymer Engineering and Science, March 2001, 41(3), 466-474].
Block copolymers of nylon 6 and poly(ethylene terephthalate) (“PET”) can be made by amide-ester interchange reactions that occur when the two polymers are blended in the melt. However, this is not a useful, well-controlled process. As the interchange reactions continue, randomization takes place [see e.g. Denchev et al, Macromol. Chem. Phys., 2001, 202(4), 574-586]. Also, the polymer chain ends play an important role in the amide-ester interchange. For example, when PET and nylon 6 are melt blended in the presence of a toluene sulfonic acid catalyst, a hydrolytic reaction of the PET occurs and produces PET chains with reactive carboxyl groups (Samperi et al, J. Polymer Sci, Part A: Polymer Chemistry, 2003, 41, 2778-2793].
U.S. Pat. No. 4,595,746, and Udipi et al [Polymer, 1997, 38(4), 927-938], describe the polymerization of caprolactam using various activating systems. However, this method is characterized by the disadvantage that, in the effort to polymerize caprolactam and a second monomer in chain growth fashion, the reactive group is continually transferred from the polymer chain end to a monomer.
Previous efforts were made to prepare block copolymers using post polymerization modification strategies. For example, Bouma, supra, modified PET and poly(butylene terephthalate) (“PBT”) with 0.1-1 mol % diamide units in an extrusion process in order to facilitate polyester crystallization. In addition, Ahn et al [Polymer, 1993, 34(10), 4156-4165] prepared polyarylate-nylon 6 block copolymers by anionic polymerization. Dihydroxy-terminated polyarylate was reacted with toluene diisocyanate, and the reaction product was in turn dissolved in and reacted with molten ε-caprolactam. When melt blended with nylon 6 and polyarylates, the block copolymer enhanced the partial miscibility of the two homopolymers. While this approach was successful in preparing block polymers containing nylon 6, the large number of post-polymerization modifications limited the commercial utility of this process.
There thus remains a need for a straightforward, industrially-viable process to prepare polyamide block copolymers.